1. Field of the Invention
The disclosure relates generally to playback control methods and systems, and, more particularly to methods and systems that automatically determine the aspect ratio of a video, and maintain the aspect ratio to play back the video.
2. Description of the Related Art
An image playback device, such as a display or a projector may have a predefined aspect ratio. When the aspect rations of a video and the image playback device are different, black borders must be added to the top and bottom, or left and right of the frames of the video. After the black borders are added to the frames, the image playback device can maintain the original aspect ratio of the video to completely play back the frames, without any cutting and loss from the frames.
For example, current movies are filmed using an aspect ratio of 2.35:1. When a movie having an aspect ratio of 2.35:1 is played back in an image playback device having a aspect ratio of 16:9, black borders must be added to the top and bottom of each frame of the movie, as shown in FIG. 1A, such that the frame can be completely displayed in the image playback device, and maintain its original aspect ratio. In this display manner, the completeness and the original aspect ratio of the frames are maintained. However, the effective display areas at the top and bottom of the image playback device are wasted due to the black borders. Therefore, a conventional practice cuts off the back borders from the frame, and enlarges the frame with black borders removed to the complete display area of the image playback device, thus obtaining a frame enlarged in the vertical direction, as shown in FIG. 1B. Then, the frame enlarged in the vertical direction is played back via an anamorphic lens, such that the frame is enlarged in the horizontal direction, returning to the original aspect ratio of 2.35:1, as shown in FIG. 1C.
However, in the conventional practice, users must determine the aspect ratio of the frames using their own naked eyes, and manually switch the image playback device to perform related operations. For example, when the aspect rations of the frames and the image playback device are different, users must indicate to the image playback device to cut off back borders from the frames. When the aspect rations of the frames and the image playback device are the same, users must indicate to the image playback device to do nothing and maintain the original frames for playback. Additionally, the anamorphic lens may be fixed or removable. When the anamorphic lens is fixed, since all frames of a video must be played and horizontally enlarged via the anamorphic lens, the displayed frames may be distorted when the video does not have an aspect ratio of 2.35:1. Further, when cut off and vertical enlargement operations are performed on the frames having an aspect ratio other than the aspect ratio of 2.35:1, frame content is lost, thus reducing the completeness of frames.